1. Field of the Invention
The present invention relates generally to a method and transportable apparatus for detecting vehicle noises and vibrations in dynamic situations. More specifically, the present invention relates to a transportable method and apparatus for detecting system imbalances in a drive line assembly for an automotive vehicle using non-contacting vibration sensors.
2. Description of the Related Art
Generally speaking, automotive vehicles require three basic components: a power plant, such as an internal combustion engine, a drive line system or drive train, as it is sometimes known in the art, and a plurality of rotatably driven wheels. A typical drive line system may include a transmission, a drive shaft and an axle connected between the engine and the driven wheels. Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the wheels and translated to the drive shaft. In turn, the drive shaft transmits rotational power from the transmission to the driven wheels via the axle assembly. The axle assembly includes a differential which is operatively coupled to the drive shaft through a pinion gear. A pair of output axle shafts connect the differential to the driven wheels.
The drive shaft typically includes an elongated tubular member which is operatively coupled to the transmission and axle assembly through a pair of universal joints or other similar coupling disposed on either end of the shaft. Alternatively, the drive shaft may include two or more elongated tubular members which are connected together by a universal joint or some other similar coupling device and connected between the transmission and axle assembly as above-discussed. Additionally, a center bearing is often employed between the transmission and axle assembly to support the drive shaft relative to the body of the vehicle.
The individual components of the drive line system discussed above often include inherent or residual imbalances due to variations in manufacturing tolerances. While steps can be taken to balance the individual components, residual imbalances often still remain. When the individual components are assembled into the drive line system, the residual imbalances can "stack up" such that they combine to produce a relatively high level of imbalance. Automotive drive line systems which embody these characteristics are unacceptable because they produce drive line vibration and boom.
It is known in the related art to balance the drive line system prior to installation into the vehicle. Many fixtures are known in the art for performing this function and typically rely on vibration measuring devices physically coupled to the drive line system to identify and thereafter correct the imbalances.
Still, this is often not enough to eliminate objectionable vibration in the drive line system of a fully assembled automotive vehicle. Thus, devices have been proposed in the related art which seek to identify and correct drive line system imbalances at the terminal stage of vehicle production and prior to shipment of the vehicle. However, these devices suffer from the disadvantage that an additional step in the manufacturing process must be added in order that vibration sensing instrumentation can be physically coupled to the drive line system of each vehicle. This is time consuming and labor intensive. In short, drive line system balancing as employed in the related art for a fully assembled automotive vehicle is presently not cost effective.
U.S. Pat. No. 5,641,904 to Kopp, et al, assigned to the assignee of the present invention ('904 patent), which is incorporated herein in its entirety, describes an apparatus which can detect and perform drive line system balancing in a fully assembled automotive vehicle in high volume production environments which is transparent to the current workload. The apparatus of the '904 patent does not rely on the physical attachment of vibration sensing instrumentation to the automotive vehicle in order to detect and correct system imbalances.
U.S. Pat. No. 5,574,226 to Reuther et al ('226 patent), assigned to the assignee of the present invention, describes a transportable four-poster facility for testing squeaks and rattles. That facility is limited to substantially vertical movement of the suspension of the vehicle and is not directed at detecting noises which occur while the vehicle is rolling.
The above methods and apparatus are useful to check vehicles at a manufacturing site, but are not practical for remote checks of Noise, Vibration, and Harshness (NVH) of a rolling vehicle. It would be desirable to perform remote NVH analysis at a dealership, remote vehicle test site, or a race track. The present invention is also useful during launch of a new model vehicle at a vehicle assembly plant. Presently, vehicle diagnosis at a dealership requires a road test to diagnose any problem, as described in the attached Ford Service Manual for a 1997 F-150 vehicle. The road test involves many variables, including road surfaces and the skill of the driver. The vehicle may also be hoisted off the ground to evaluate the driveline, but this may unload the driveline and therefore reduce the magnitude of the problem and hinder detection thereof. The tests are time consuming and may require several iterations before the concern is detected and corrected. It would therefore be desirable to provide a vehicle test apparatus which is transportable and one which provides for accurate and rapid detection of NVH concerns.